Sonic Adventure 2, in the Dark Story before the Egg Golem boss. We get almost the same cutscene as when you fight it as Sonic, but in this version Sonic jumps up and delivers a kick to the golem which breaks the restraining mechanism on it and causes it to turn on Eggman. Though it's more of the dialogue that makes this a Crowning Moment of Funny:
Eggman: *When the Golem turns towards him* NOOOOOOOOOOO!
Made funnier by the fact that if you listen to it with the Japanese audio, it becomes "TEEEEEERIAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA!"
Three words: Amy. Hugging. Shadow. The look on his face is priceless.